Search

For sheer complexity, braincases are generally considered anatomically conservative. However, recent research on the braincases of tyrannosaurids have revealed extensive morphological variations. This line of inquiry has its root in Dale Russell’s review of tyrannosaurids in which he established Daspletosaurus torosus — a large tyrannosaurine from the Campanian of southern Alberta. In the wake of systematic revisions to tyrannosaurines previously assigned to Daspletosaurus, one potentially distinct species remains undescribed. This paper describes and compares a braincase referable to this species with that of the holotype for Daspletosaurus torosus using computerized-tomography-based reconstructions. The two braincases have numerous differences externally and internally. The specimen of Daspletosaurus sp. has a bottlenecked olfactory tract, short and vertical lagena, and a developed ascending column of the anterior tympanic recess. The holotype of Daspletosaurus torosus has many unusual traits, including an anteriorly positioned trochlear root, elongate common carotid canal, distinct chamber of the basisphenoid recess, asymmetry in the internal basipterygoid aperture, and laterally reduced but medially expanded subcondylar recess. This comparison also identified characters that potentially unite the two species of Daspletosaurus, including deep midbrain flexures in the endocasts. However, many character variations in the braincases are known in other tyrannosaurids to correlate with body size and maturity, or represent individual variations. Therefore, taxonomic and phylogenetic signals can be isolated from background variations in a more comprehensive approach by using additional specimens. New information on the two braincases of Daspletosaurus is consistent with the emerging view of tyrannosaurid braincases as highly variable, ontogenetically dynamic character complexes.

An associated incomplete skeleton of a ceratopsid dinosaur from the Campanian deposits of the Allison Member of the Menefee Formation in New Mexico, USA is described. Although it was originally described over two decades ago, newly prepared portions of the Menefee Formation skeleton and reinterpretations of previously known morphology, in addition to newly described specimens have provided new information on ceratopsids, and centrosaurines in particular. These new data allow for a thorough reassessment of the specimen and the erection of a new taxon: Menefeeceratops sealeyi gen. et sp. nov., potentially the oldest recognized member of Centrosaurinae. Menefeeceratops sealeyi is represented by diagnostic cranial and postcranial skeletal elements. The cranial elements include a portion of the left premaxilla, a nearly complete left postorbital horncore, a parietal fragment, the right and left squamosals, the left jugal, the predentary, and the left dentary. Postcranial material consists of two cervical vertebrae, eight dorsal vertebrae, a partial sacrum with six sacral vertebrae, 11 dorsal ribs, the distal left radius, proximal and distal portions of the left ulna, the left femur, and a left metatarsal II. The taxonomic validity of Menefeeceratops sealeyi is supported by a combination of several morphological characters. These include a lack of epiossifications on the lateroposterior edge of the parietal (shared with Machairoceratops), three epiossifications on the squamosal, and three smaller, secondary undulations as part of episquamosal locus S1. There are also two subequal embayments on the posterior free margin of the squamosal with the more dorsal embayment (between episquamosal loci 1 and 2) distinctly larger than the ventral (= lateroventral) one (between episquamosal loci 2 and 3), three ridges on the lateral (dorsolateral) surface of the squamosal, an elongate posterior portion of the squamosal, the presence of a shallow but distinct groove on the medial surface of the squamosal nearly paralleling the ventrolateral and ventroposterior edges, elongate postorbital (= supraorbital) horns that are anteriorly curved distally, and two elongate ridges on the lateral surface of the dentary that diverge anteriorly, creating a distinct anterior triangular fossa. Phylogenetic analysis of Menefeeceratops sealeyi places this new species as a basal centrosaurine, most closely related to Crittendenceratops krzyzanowskii, thus adding to the growing record of centrosaurines discovered in western North America. It thus provides new information about the diversity of morphologies throughout different species and the temporal and paleobiogeographic distribution of these animals throughout Laramidia during the Late Cretaceous. Its presence as one of the, if not the, oldest members of the Centrosaurinae also suggests centrosaurines originated in the southern portions of western North America and the southern Rocky Mountain region, and subsequently radiated north during the upper middle to late Campanian.

A rare early Campanian (Aquilan) assemblage consisting of disarticulated anuran bones is described from the Aguja Formation of West Texas, USA. Many specimens within the assemblage pertain to taxonomically informative elements (maxillae, urostyles, and ilia). Morphological variety among specimens pertaining to each suggests high local species richness comparable with that seen elsewhere among frogs from similarly well-sampled localities of the Late Cretaceous Western Interior. Comparison between environmentally and temporally analogous microvertebrate assemblages in southern Utah, USA, reveals that anurans in both areas exhibit morphological similarities consistent with regionally allied ‘southern’ faunas. Among their differences, one character (dorsal protuberance of the ilium) consistently exhibited among some ilial morphotypes from Utah is conspicuously absent among those of West Texas. Two ostensibly exclusive ilial morphs in West Texas add additional support to the presence of taxonomically segregated, sub-regional populations of anurans in southern Laramidia during early to middle Campanian time.

The Lowerverse local fauna of West Texas, USA, preserves a rare, early Campanian assemblage of microvertebrates from Laramidia. The recovery of 137 fragmentary specimens reveals that albanerpetontids were locally abundant here and also widespread throughout much of the Western Interior of North America by early Campanian time. Both gracile- and robust-snouted species are represented within the assemblage. Among these, the occurrence of Albanerpeton nexuosum is consistent with its occurrence in paracontemporaneous deposits elsewhere in the Western Interior. The referral of two specimens to Albanerpeton sp., cf. Albanerpeton galaktion, strongly suggests that this long-lived taxon was far more widespread during the early Campanian than previously known and its likely occurrence in West Texas represents a significant geotemporal range extension for the species. However, Albanerpeton gracile is seemingly restricted to Judithian “age” deposits in North America and was not identified at Lowerverse. The Lowerverse assemblage supports the current paradigm involving the occurrence of these three named albanerpetontids during middle Campanian – Maastrichtian time in the Western Interior of North America.

Late Cretaceous dinosaur assemblages of North America—characterized by gigantic tyrannosaurid predators, and large-bodied herbivorous ceratopsids and hadrosaurids—were highly successful from around 80 million years ago (Ma) until the end of the ‘Age of Dinosaurs’ 66 Ma. However, the origin of these iconic faunas remains poorly understood because of a large, global sampling gap in the mid-Cretaceous, associated with an extreme sea-level rise. We describe the most complete skeleton of a predatory dinosaur from this gap, which belongs to a new tyrannosauroid theropod from the Middle Turonian (~92 Ma) of southern Laramidia (western North America). This taxon, Suskityrannus hazelae gen. et sp. nov., is a small-bodied species phylogenetically intermediate between the oldest, smallest tyrannosauroids and the gigantic, last-surviving tyrannosaurids. The species already possesses many key features of the tyrannosaurid bauplan, including the phylogenetically earliest record of an arctometatarsalian foot in tyrannosauroids, indicating that the group developed enhanced cursorial abilities at a small body size. Suskityrannus is part of a transitional Moreno Hill (that is, Zuni) dinosaur assemblage that includes dinosaur groups that became rare or were completely absent in North America around the final 15 Myr of the North American Cretaceous before the end-Cretaceous mass extinction, as well as small-bodied forebears of the large-bodied clades that dominated at this time. Suskityrannus hazelae gen. et sp. nov. is a small-bodied tyrannosauroid that bridges the gap between earlier, smaller tyrannosauroids and the gigantic, last-surviving tyrannosaurids of the terminal Cretaceous.

Turtles are typically important members of Late Cretaceous vertebrate assemblages throughout North America, and are considered a useful tool to define biogeographic patterns. In Mexico, Cretaceous turtles have been recorded in the states of Baja California, Chiapas, Chihuahua, Coahuila, Nuevo León, Puebla, and Sonora; specifically the state of Coahuila shows so far, the highest diversity of turtles. In this paper, the diversity of Late Cretaceous turtles from the El Gallo Formation (Baja California) is reviewed. Previously, only Naomichelys speciosa was recognized in this Formation. Based on fragments with distinctive sculpture patterns four additional taxa are recognized, Compsemys victa, Basilemys sp., Trionychidae indet., and cf. Chelydridae. With the recognition of these new taxa, the knowledge of Cretaceous turtles diversity of the El Gallo Formation is increased. This assemblage is unusual compared to other North American turtle assemblages because it suggests the presence of previously unrecognized biogeographic patterns. Here we report the first record of Basilemys sp. from the Late Cretaceous of Mexico and the presence of cf. Chelydridae on the western side of Laramidia. Fil: López Conde, Oliver Ariel. Universidad Nacional Autónoma de México; México Fil: Sterli, Juliana. Museo Paleontologico Egidio Feruglio; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Chavarría Arellano, María L.. Universidad Nacional Autónoma de México; México Fil: Brinkman, Donald B.. Museo Tyrrell; Canadá Fil: Montellano Ballesteros, Marisol. Universidad Nacional Autónoma de México; México

During the Cretaceous period, North America was divided into two landmasses, the eastern Appalachia and western Laramidia. Recent research on several sites scattered across the eastern margin of North America has allowed for the analysis of vertebrate faunas from the once obscure terrestrial fossil record of Appalachia, revealing the landmass harbored a distinctive fauna composed of mostly relict forms. One geological unit that has produced a comparatively extensive record of terrestrial vertebrates, including non-avian dinosaurs, is the middle Campanian Tar Heel Formation of North Carolina. Here, the first definitive occurrence of a dromaeosaurid from the Tar Heel Formation is reported on the basis of a tooth from a fairly large member of that group. This tooth clusters with those of dromaeosaurine dromaeosaurids from the western United States and Canada in morphometric analysis, differing in morphology and size from other dromaeosaurid teeth from southeastern North America that have been assigned to saurornitholestines or considered indeterminate. The tooth described herein is intermediate in size between those of smaller dromaeosaurids like Saurornitholestes and gigantic forms like Dakotaraptor, filling the gap between larger- and smaller-bodied dromaeosaurids from the Late Cretaceous.

The neosuchianDeinosuchusis known from numerous localities throughout the Campanian of North America, from New Jersey to Montana (USA) and as far south as Coahuila (Mexico). Here we describe six osteoderms, two vertebrae, and a partial tooth discovered in the Menefee Formation of New Mexico and assign them toDeinosuchussp., representing one of the earliest occurrences of this genus on the Laramidian subcontinent, and among the earliest known occurrences of this large alligatoroid in all of North America. The osteoderms are morphologically distinct in their inflated construction, with deep and radially distributed pitting, which closely matches osteoderms ofDeinosuchus.

Tyrannosaurids are hypothesized to be gregarious, possibly parasocial carnivores engaging in cooperative hunting and extended parental care. A tyrannosaurid (cf.Teratophoneus curriei) bonebed in the late Campanian age Kaiparowits Formation of southern Utah, nicknamed the Rainbows and Unicorns Quarry (RUQ), provides the first opportunity to investigate possible tyrannosaurid gregariousness in a taxon unique to southern Laramidia. Analyses of the site’s sedimentology, fauna, flora, stable isotopes, rare earth elements (REE), charcoal content and taphonomy suggest a complex history starting with the deaths and transport of tyrannosaurids into a peri-fluvial, low-energy lacustrine setting. Isotopic and REE analyses of the fossil material yields a relatively homogeneous signature indicating the assemblage was derived from the same source and represents a fauna living in a single ecospace. Subsequent drying of the lake and fluctuating water tables simultaneously overprinted the bones with pedogenic carbonate and structurally weakened them through wet-dry cycling. Abundant charcoal recovered from the primary bone layer indicate a low temperature fire played a role in the site history, possibly triggering an avulsion that exhumed and reburied skeletal material on the margin of a new channel with minimal transport. Possible causes of mortality and concentration of the tyrannosaurids include cyanobacterial toxicosis, fire, and flooding, the latter being the preferred hypothesis. Comparisons of the RUQ site with other North American tyrannosaur bonebeds (Dry Island-Alberta;Daspletosaurus horneri-Montana) suggest all formed through similar processes. Combined with ichnological evidence, these tyrannosaur mass-burial sites could be part of an emerging pattern throughout Laramidia reflecting innate tyrannosaurid behavior such as habitual gregariousness.

Dromaeosaurids (Theropoda: Dromaeosauridae), a group of dynamic, swift predators, have a sparse fossil record, particularly at the time of their extinction near the Cretaceous-Paleogene boundary. Here we report on a new dromaeosaurid, Dineobellator notohesperus, gen. and sp. nov., consisting of a partial skeleton from the Upper Cretaceous (Maastrichtian) of New Mexico, the first diagnostic dromaeosaurid to be recovered from the latest Cretaceous of the southern United States (southern Laramidia). The holotype includes elements of the skull, axial, and appendicular skeleton. The specimen reveals a host of morphologies that shed light on new behavioral attributes for these feathered dinosaurs. Unique features on its forelimbs suggest greater strength capabilities in flexion than the normal dromaeosaurid condition, in conjunction with a relatively tighter grip strength in the manual claws. Aspects of the caudal vertebrae suggest greater movement near the tail base, aiding in agility and predation. Phylogenetic analysis places Dineobellator within Velociraptorinae. Its phylogenetic position, along with that of other Maastrichtian taxa (Acheroraptor and Dakotaraptor), suggests dromaeosaurids were still diversifying at the end of the Cretaceous. Furthermore, its recovery as a second North American Maastrichtian velociraptorine suggests vicariance of North American velociraptorines after a dispersal event during the Campanian-Maastrichtian from Asia. Features of Dineobellator also imply that dromaeosaurids were active predators that occupied discrete ecological niches while living in the shadow of Tyrannosaurus rex, until the end of the dinosaurs’ reign.

Daspletosaurini clade nov. ZOOBANK ID: urn:lsid:zoobank.org:act: B9FCE1A0-B6B7-41E4- 95C0-44F17E34C118 Definition. The most inclusive clade that includes all taxa closer to Daspletosaurus torosus than to Albertosaurus sarcophagus, Alioramus remotus, Teratophoneus curriei, or Tyrannosaurus rex. Diagnosis. Daspletosaurini is diagnosed by the presence of an extremely coarse subcutaneous surface of the maxilla anteroventral to the antorbital fossa; a constricted jugal ramus of the maxilla; the anteroventral corner of the maxilla tapers into a shallow angle (< 69) as measured between the alveolar margin of the first two alveoli and the anterior margin of the subcutaneous surface; a prefrontal that is broad in dorsal view and strongly dorsomedially arced in anterior view; and a dentary chin located ventral to either the third alveolus or third interdental plate. Daspletosaurins also differ from all other tyrannosaurines of subadult/adult size, except alioramins, in having no fewer than 14 maxillary teeth (see Carr et al., 2017). Included taxa. Daspletosaurus torosus Russell (1970), Daspletosaurus horneri Carr et al. (2017), and Thanatotheristes degrootorum gen. et. sp. nov., Published as part of Voris, Jared T., Therrien, Fran��ois, Zelenitsky, Darla K. & Brown, Caleb M., 2020, A new tyrannosaurine (Theropoda: Tyrannosauridae) from the Campanian Foremost Formation of Alberta, Canada, provides insight into the evolution and biogeography of tyrannosaurids, pp. 1-15 in Cretaceous Research 110 (104388) on page 3, DOI: 10.1016/j.cretres.2020.104388, http://zenodo.org/record/3672003, {"references":["Carr, T. D., Varricchio, D. J., Sedlmayr, J. C., Roberts, E. M., Moore, J. R., 2017. A new tyrannosaur with evidence for anagenesis and crocodile-like facial sensory system. Scientific Reports 7, 1 e 11. https: // doi. org / 10.1038 / srep 44942.","Russell, D. A., 1970. Tyrannosaurs from the Late Cretaceous of western Canada. National Museum of Natural Sciences Publications in Palaeontology No. 1. Queen' s Printer, Ottawa, Ont., pp. 1 e 34"]}

The horned dinosaurs (Ceratopsidae) were a diverse family of herbivorous dinosaurs originating in the Late Cretaceous in western North America (Laramidia). As one of the most species-rich dinosaur groups, their diversity and distribution are important to understanding Cretaceous dinosaur evolution. Ceratopsids have previously been hypothesized to have high levels of endemism despite inhabiting a relatively small land mass with few barriers to dispersal. Here, we document a new chasmosaurine ceratopsid, Sierraceratops turneri gen. et sp. nov., from the Upper Cretaceous (uppermost Campanian–Maastrichtian) Hall Lake Formation of south-central New Mexico, consistent with the hypothesis that southern Laramidia supported an endemic dinosaur fauna. Sierraceratops is distinguished by its relatively short, robust, and mediolaterally compressed postorbital horns; a flattened medial ridge on the posterior end of the pterygoid; a jugal with pronounced anterior flanges; a long pyramid-shaped epijugal horncore; a D-shaped cross section of the median parietal bar; and a squamosal with a pointed tip and low episquamosal ossifications. Phylogenetic analysis recovers Sierraceratops as sister to Bravoceratops and Coahuilaceratops, part of a clade endemic to the southwestern United States and Mexico. Sierraceratops adds to the diversity and disparity of the Chasmosaurinae in the Late Cretaceous and provides additional evidence for Laramidian endemism. Together with Sierraceratops, the Hall Lake Formation dinosaur fauna suggests that the latest Cretaceous of southern Laramidia was characterized by endemic clades and distinct community structures.

The sparse dinosaur record of eastern North America has rendered the dinosaurs of the Late Cretaceous landmass of Appalachia obscure. Appalachia may have been a refugium for dinosaur species that would be replaced on Appalachia's western contemporary, Laramidia, from which the former landmass was isolated by the Western Interior Seaway. Among the theropods of the landmass, Appalachian tyrannosaurs are only represented currently by the two valid taxa Dryptosaurus aquilunguis and Appalachiosaurus montgomeriensis, a distinct but indeterminate taxon from the Campanian of Delaware, and indeterminate skeletons and isolated elements. New Jersey in particular has rendered many bones assignable to tyrannosauroids, contributing much to the study of members of this clade from Appalachia. Here, the partial tibia of a tyrannosauroid is described from the Maastrichtian Navesink Formation of Monmouth County, New Jersey. The specimen, originally described by paleontologists Edward Drinker Cope and Joseph Leidy, is important for revealing further the theropod fauna of the Navesink Formation of New Jersey and being the second definite occurrence of a tyrannosauroid in eastern North America during the Maastrichtian, thus illuminating the group's ecology and biogeography during that stage of the Cretaceous. Phylogenetic analysis plots the Navesink specimen as the sister taxon to Bistahieversor in a larger polytomy of all tyrannosauroids more derived than Eotyrannus, suggesting that the Navesink bone may represent either another “intermediate”-grade tyrannosauroid from Appalachia or a relative of B. sealeyi that migrated to eastern North America after the regression of the Western Interior Seaway.

Isolated bones and osteoderms of ankylosaurian dinosaurs recovered from Late Cretaceous sediments of northern Coahuila, northeastern Mexico, have been identified as remains of nodosaurids. Here, we summarize these discoveries and provide a review on Mexican Ankylosauria from a taxonomic perspective. We also present a new taxon, Acantholipan gonzalezi gen. et sp. nov. from the Pen Formation and provide a phylogenetic analysis integrating the new taxon. A. gonzalezi is the first named ankylosaur from Mexico that adds to the currently rare nodosaurid diversity from southern Laramidia.

Premise of research. Over the past 3 decades, angiosperm woods have been reported from the Campanian to the Maastrichtian of southern Laramidia, including Coahuila and Chihuahua, Mexico; Big Bend N...

Fossil characiform dentaries from the “Lowerverse locality” in the lower Campanian portion of the Aguja Formation of West Texas represent a rare Late Cretaceous occurrence of characiform fishes in North America. Two morphotypes are represented. Both of them exhibit ventrally encased, mandibular laterosensory canals and distinctive anterior lobes unique to the characiform symphyseal ‘hinge’. The first, dentigerous morphotype closely resembles fossil characiform dentaries from the Campanian Dinosaur Park Formation of Alberta, Canada. All of these are collectively referred herein to Primuluchara laramidensis gen et sp. nov. The second morph is edentulous as in extant curimatids and pertains to a different new species herein referred to Eotexachara malateres gen et sp. nov. Numerous Weberian vertebral centra recovered at Lowerverse suggest that characiforms were abundant in the coastal, subaquatic paleoenvironment here. The early Campanian age of the Aguja Formation characiforms supports previous temporal estimates regarding the arrival of characiforms in North America from either Europe or South America as inferred from previous molecular and/or paleontological studies. The presence of morphologically related, but geotemporally divergent species in Campanian strata of West Texas and Alberta indicates a south-to-north radiation among Laramidian characiforms and points to a southerly origin for ancestral forms. Santonian – Maastrichtian occurrences of characiforms in Europe suggests that they reached the limit of their dispersal there and were unable to invade southern Laramidia by the early Campanian. Whether the likely dispersal of characiforms from South America occurred via an archaeo- or telolimnitic progression remains unclear. However, it is plausible that euryhalinity played some role in their coastal dispersal.

In order for palaeontological data to be informative to ecologists seeking to understand the causes of today's diversity patterns, palaeontologists must demonstrate that actual biodiversity patterns are preserved in our reconstructions of past ecosystems. During the Late Cretaceous, North America was divided into two landmasses, Laramidia and Appalachia. Previous work has suggested strong faunal provinciality on Laramidia at this time, but these arguments are almost entirely qualitative. We quantitatively investigated faunal provinciality in ceratopsid and hadrosaurid dinosaurs using a biogeographic network approach and investigated sampling biases by examining correlations between dinosaur occurrences and collections. We carried out a model-fitting approach using generalized least-squares regression to investigate the sources of sampling bias we identified. We find that while the raw data strongly support faunal provinciality, this result is driven by sampling bias. The data quality of ceratopsids and hadrosaurids is currently too poor to enable fair tests of provincialism, even in this intensively sampled region, which probably represents the best-known Late Cretaceous terrestrial ecosystem on Earth. To accurately reconstruct biodiversity patterns in deep time, future work should focus on smaller scale, higher resolution case studies in which the effects of sampling bias can be better controlled.

Ankylosaurus magniventris is an iconic dinosaur species often depicted in popular media. It is known from relatively fragmentary remains compared with its earlier and smaller relatives such as Euoplocephalus and Anodontosaurus. Nevertheless, the known fossils of Ankylosaurus indicate that it had diverged significantly in cranial and postcranial anatomy compared with other Laramidian ankylosaurines. In particular, the dentition, narial region, tail club, and overall body size differ substantially from other Campanian–Maastrichtian ankylosaurines. We review the anatomy of this unusual ankylosaur using data from historic and newly identified material and discuss its palaeoecological implications.

The Dinosaur Park Formation (DPF) has a diverse assemblage of chasmosaurines currently represented by Chasmosaurus belli, C. russelli, Vagaceratops irvinensis, and Mercuriceratops gemini, and may also include remains possibly referable to Spiclypeus shipporum. Two skulls, YPM 2016 and AMNH 5402, previously referred to C. belli, both have a straight posterior parietal bar with five epiparietals present (YPM 2016) or inferred (AMNH 5402) on each side – the combination of which is unique to V. irvinensis. Based on our new morphological observations and interpretations of these two skulls, we recover V. irvinensis as a species of Chasmosaurus (C. irvinensis), although the interrelationships between C. irvinensis, C. belli, and C. russelli remain unclear. We refrain from formerly assigning YPM 2016 and AMNH 5402 to C. irvinensis, however, as their parietal fenestrae are significantly larger and their epiparietals are significantly shorter than those of C. irvinensis; instead, we reassign these two skulls to Chasmosaurus sp. Given the low stratigraphic position of YPM 2016 (unknown in AMNH 5402) relative to C. irvinensis, we believe this specimen to represent a basal member of the lineage leading to C. irvinensis. If our assessment is correct, this would indicate that the C. irvinensis lineage has a large degree of stratigraphic overlap with that of C. belli and C. russelli. The close phylogenetic relationship and supposed stratigraphic separation for these three taxa reported in previous studies were used to suggest that they may represent an anagenetic lineage, whereby C. russelli evolved into C. belli, and C. belli evolved into, and was entirely replaced by, the latter. However, the lack of stratigraphic separation between these three taxa indicates that they instead arose via cladogenesis.

Pterosaurs were widespread during the Late Cretaceous, but their fossils are comparatively rare in terrestrial depositional environments. A large pterosaur bone from the Kaiparowits Formation (late Campanian, ~76–74 Ma) of southern Utah, USA, is tentatively identified as an ulna, although its phylogenetic placement cannot be precisely constrained beyond Pterosauria. The element measures over 36 cm in preserved maximum length, indicating a comparatively large individual with an estimated wingspan between 4.3 and 5.9 m, the largest pterosaur yet reported from the Kaiparowits Formation. This size estimate places the individual at approximately the same wingspan as the holotype forCryodrakon boreasfrom the penecontemporaneous Dinosaur Park Formation of Alberta. Thus, relatively large pterosaurs occurred in terrestrial ecosystems in both the northern and southern parts of Laramidia (western North America) during the late Campanian.

I describe the assemblage of baenid turtles found in the Campanian Kaiparowits Formation of southern Utah and compare it with baenids from other basins across Laramidia. Baenids were one of the most diverse and abundant freshwater turtle clades during the Late Cretaceous. They were restricted to North America, with all except the basal-most taxon (Arundelemys) restricted to Laramidia. During the Campanian, baenids were conspicuous parts of the turtle assemblages of Alberta, Montana and New Mexico. The baenids of the Kaiparowits Formation are critical in that they provide an assemblage from southern Laramidia that is correlative with those from northern Laramidia, allowing for more accurate testing of Campanian palaeobiogeographical hypotheses. In this paper, two new baenid species, Neurankylus hutchisoni sp. nov. and Neurankylus utahensis sp. nov., are described. Additionally, the first description of cranial material from Denazinemys nodosa is provided. A comprehensive survey of collected material indica...

A diverse microfauna from the lower shale of the Aguja Formation of West Texas records a rare, early Campanian assemblage of fossil squamates from North America. This assemblage is comprised of scincomorph, anguimorph, and ophidian taxa and is the most inclusive of its kind thus far described from the southern faunal province of Laramidia. Among numerous taxa described herein, three (Hypostylos lehmani gen. et sp. nov., Bothriagenys flectomendax sp. nov., and Hydrargysaurus gladius gen. et sp. nov) pertain to new scincomorphs which dominate the assemblage; however, subordinate anguimorphs are also well-represented. Snakes are represented by a single taxon, aff. Coniophis; a species seemingly ubiquitous throughout most Campanian strata in the southern Western Interior. Comparison among squamate assemblages from similar coastal facies in the upper shale of the Aguja Formation as well as the paracontemporaneous Wahweap and Kaiparowits formations of southern Utah reveals patterns of biogeographic segregation among some lizard species and the presence of two distinct communities. These two ‘southern’ squamate faunas are likely the result of variables involving climate and eustacy which facilitated diversity as well as the development of sub-provincial quarters of endemism during early-middle Campanian time.

Lithostratigraphic investigation of the richly fossiliferous Kaiparowits Formation in southern Utah reveals the presence of a previously unidentified stratigraphic unit herein named the Upper Valley Member. The 255-m-thick Upper Valley Member is latest Campanian to earliest Maastrichtian in age and records a significant sedimentological change in the Kaiparowits Formation. This change is illustrated in the member by a significant increase in near syn-sedimentary aged zircons, coincident with the introduction of white, volcaniclastic sandstones, as well as a paucity of Jurassic grains, which dominate the provenance of the rest of the formation. The source of the late Campanian volcaniclastic material, including near syn-sedimentary zircons, is most likely from nearby volcanic centers within the Laramide porphyry copper province to the south of the Kaiparowits Plateau in the Mogollon region. Measured sections reported here stratigraphically expand the Kaiparowits Formation to a total of 1005 m and find that the upper boundary of the formation is largely gradational with the overlying Canaan Peak Formation. Lithological changes documented in this study are interpreted to signify a sedimentological response to proximal magmatism and emerging uplifts within the Cordilleran foreland basin during early Laramide orogenesis, which resulted in paleo-drainage rearrangement in southern Laramidia in the latest Campanian. The fossil-bearing Upper Valley Member can be correlated regionally to the Kirtland, Tuscher and Bearpaw formations and other latest Campanian – and possibly early Maastrichtian – units across western North America and represents the capping member one of the most continuous terrestrial records of the Campanian biosphere found anywhere in the world.

Chasmosaurine ceratopsids are well documented from the Upper Cretaceous (Campanian) Dinosaur Park Formation (DPF) of southern Alberta and Saskatchewan, and includeChasmosaurus belli,Chasmosaurus russelli,Mercuriceratops gemini,Vagaceratops irvinensis, and material possibly referable toSpiclypeus shipporum.In this study, we describe three recently prepared chasmosaurine skulls (CMN 8802, CMN 34829, and TMP 2011.053.0046) from the DPF, and age-equivalent sediments, of Alberta. CMN 8802 and CMN 34829 are both referred toChasmosaurussp. based on the size and shape of the preserved parietal fenestrae. TMP 2011.053.0046 is referred toVagaceratopssp. based on the position and orientation of its preserved epiparietals. Each skull is characterized by the presence of an accessory fenestra in either the squamosal (CMN 8802 and TMP 2011.053.0046) or parietal (CMN 34829). Such fenestrae are common occurrences in chasmosaurine squamosals, but are rare in the parietal portion of the frill. The origin of the fenestrae in these three specimens is unknown, but they do not appear to exhibit evidence of pathology, as has been previously interpreted for the accessory fenestrae in most other chasmosaurine frills. These three skulls contribute to a better understanding of the morphological variation, and geographic and stratigraphic distribution, of chasmosaurines within the DPF and age-equivalent sediments in Western Canada.

A large osteoderm found in a channel sandstone in the Williams Fork Formation (“Mesaverde Group”) of northwestern Colorado represents the first reported evidence of a large neosuchian crocodyliform in the formation in northwestern Colorado. The osteoderm is of a size and pit pattern that resembles the large alligatoroid Deinosuchus but the thickness and shape of the bone suggest possible affinities with the goniopholidid or pholidosaurid crocodyliform material known from the Campanian of southern Utah; smaller, similar osteoderms from the formation may suggest that this form was relatively abundant as juveniles. Overall faunal similarities of the Williams Fork Formation are closest to the Kaiparowits Formation of southern Utah also, but few lower level taxa can be confirmed from the Williams Fork that are not also known from other areas north and south, suggesting that the Williams Fork vertebrate fauna comes from the southern end of a transition zone between possible latitudinal provinces of Laramidia.

Maastrichtian terrestrial deposits throughout Laramidia (western North America) have yielded a wealth of ancient dinosaur diversity. Yet, despite intense collecting in some areas, latitudinal sampling unevenness still limits biogeographic studies, making new records of dinosaur occurrences significant. Here, we describe the first non-dental pachycephalosaurid cranial material from the late Maastrichtian Scollard Formation of central Alberta, Canada, which allows more precise taxonomic identification of pachycephalosaurids from the northern part of the Western Interior Basin during this time interval. A domed parietal, although weathered, retains several features that allow it to be referred to the tribe Pachycephalosaurini within the subfamily Pachycephalosaurinae, and likely to the genus Pachycephalosaurus. This specimen provides further support for the suggestion that late Maastrichtian dinosaur communities were generally cosmopolitan with no discrete faunal provinces in Laramidia, and underscores the importance of collecting fragmentary, but identifiable remains that often go unreported.

During the Late Cretaceous, the continent of North America was divided into two sections: Laramidia in the west and Appalachia in the east. Although the sediments of Appalachia recorded only a sparse fossil record of dinosaurs, the dinosaur faunas of this landmass were different in composition from those of Laramidia. Represented by at least two taxa (Appalachiosaurus montgomeriensis and Dryptosaurus aquilunguis), partial and fragmentary skeletons, and isolated bones, the non-tyrannosaurid tyrannosauroids of the landmass have attracted some attention. Unfortunately, these eastern tyrants are poorly known compared to their western contemporaries. Here, one specimen, the partial metatarsus of a tyrannosauroid from the Campanian Merchantville Formation of Delaware, is described in detail. The specimen can be distinguished from A. montgomeriensis and D. aquilunguis by several morphological features. As such, the specimen represents a potentially previously unrecognized taxon of tyrannosauroid from Appalachia, increasing the diversity of the clade on the landmass. Phylogenetic analysis and the morphology of the bones suggest the Merchantville specimen is a tyrannosauroid of “intermediate” grade, thus supporting the notion that Appalachia was a refugium for relict dinosaur clades.

The article discusses the discovery of fossil evidence of distinct communities of large dinosaurs from the Late Cretaceous period in an area of the western U.S. once comprising the Laramidia landmass, focusing on an excavation at the Kaiparowits Formation in Utah. Scientists have questioned how these dinosaurs could have coexisted in such a small geographical area, as the large body sizes and species diversity indicated by the fossils should have been constrained by the available resources in their home range. It is suggested that dinosaurs may have had a lower metabolic rate than previously thought, or that Late Cretaceous vegetation was more abundant, diverse, or nutritious than present-day plants in the area. INSETS: Dinosaur Diversity;Dinosaur Diversity.

Using the megaherbivorous dinosaur assemblage from the Dinosaur Park Formation as a model, linear and geometric morphometrics are applied to examine the degree to which different feeding styles—as reflected by beak morphology—facilitated the coexistence of these animals on the Late Cretaceous island continent of Laramidia. Our findings indicate that megaherbivorous dinosaurs occupied a spectrum of feeding habits. The wide, square beaks of the ankylosaurs suggest that these animals were bulk-feeders that consumed more fibrous herbage than traditionally assumed. Conversely, the narrow, square beaks of the ceratopsids evoke concentrate feeders, although the large body sizes and sophisticated dental batteries of these animals suggest a diet of forbs and low-growing scrub, akin to the feeding strategy of the black rhinoceros (Diceros bicornis). Both nodosaurids and hadrosaurids had beaks of intermediate size and shape, suggesting that these were mixed feeders that consumed a diversity of plant types of variable nutritional quality. Contrary to previous suggestions, there is little evidence for different feeding styles within the aforementioned families. Feeding styles were evolutionarily stable, and lend further support to the contention that the fossil assemblage of the Belly River Group constitutes a chronofauna.

We describe a new genus and species of hadrosaurid dinosaur, Latirhinus uitstlani, from upper Campanian strata of the Cerro del Pueblo Formation in northern Mexico. The new taxon differs from other hadrosaurids, except Gryposaurus, in possessing a deep and arcuate dorsal process of the nasal; it differs from Gryposaurus, as well as from all other saurolophines, in having a broader narial foramen, and an anterodorsally curved deltoid crest of the scapula (convergent with Lambeosaurinae within the context of Hadrosauridae). L. uitstlani appears to be allied to ‘kritosaurs’, particularly to species of Gryposaurus, and it represents one of the southernmost saurolophines of North America. Likewise, L. uitstlani adds to the diversity of saurolophines in the southern Western Interior Basin and its occurrence in northern Mexico is consistent with the apparent predominance of ‘kritosaurs’ in southern Laramidia during late Campanian times.

A new species of tyrannosaurid from the upper Two Medicine Formation of Montana supports the presence of a Laramidian anagenetic (ancestor-descendant) lineage of Late Cretaceous tyrannosaurids. In concert with other anagenetic lineages of dinosaurs from the same time and place, this suggests that anagenesis could have been a widespread mechanism generating species diversity amongst dinosaurs, and perhaps beyond. We studied the excellent fossil record of the tyrannosaurid to test that hypothesis. Phylogenetic analysis places this new taxon as the sister species to Daspletosaurus torosus. However, given their close phylogenetic relationship, geographic proximity, and temporal succession, where D. torosus (~76.7–75.2 Ma) precedes the younger new species (~75.1–74.4 Ma), we argue that the two forms most likely represent a single anagenetic lineage. Daspletosaurus was an important apex predator in the late Campanian dinosaur faunas of Laramidia; its absence from later units indicates it was extinct before Tyrannosaurus rex dispersed into Laramidia from Asia. In addition to its evolutionary implications, the texture of the facial bones of the new taxon, and other derived tyrannosauroids, indicates a scaly integument with high tactile sensitivity. Most significantly, the lower jaw shows evidence for neurovasculature that is also seen in birds.

The Upper Cretaceous (middle-late Campanian) Wahweap Formation of southern Utah contains the oldest diagnostic evidence of ceratopsids (to date, all centrosaurines) in North America, with a number of specimens recovered from throughout a unit that spans between 81 and 77 Ma. Only a single specimen has been formally named, Diabloceratops eatoni, from the lower middle member of the formation. Machairoceratops cronusi gen. et sp. nov., a new centrosaurine ceratopsid from the upper member of the Wahweap Formation, is here described based on cranial material representing a single individual recovered from a calcareous mudstone. The specimen consists of two curved and elongate orbital horncores, a left jugal, a nearly complete, slightly deformed braincase, the left squamosal, and a mostly complete parietal ornamented by posteriorly projected, anterodorsally curved, elongate spikes on either side of a midline embayment. The fan-shaped, stepped-squamosal is diagnostic of Centrosaurinae, however, this element differs from the rectangular squamosal in Diabloceratops. Machairoceratops also differs in the possession of two anterodorsally (rather than laterally) curved epiparietal ornamentations on either side of a midline embayment that are distinguished by a posteromedially-oriented sulcus along the entire length of the epiparietal. Additionally, the parietosquamosal frill is lacking any other epiossifications along its periphery. Machairoceratops shares a triangular (rather than round) frill and spike-like epiparietal loci (p1) ornamentation with the stratigraphically lower Diabloceratops. Both parsimony and Bayesian phylogenetic analyses place Machairoceratops as an early-branching centrosaurine. However, the parsimony-based analysis provides little resolution for the position of the new taxon, placing it in an unresolved polytomy with Diabloceratops. The resultant Bayesian topology yielded better resolution, aligning Machairoceratops as the definitive sister taxon to a clade formed by Diabloceratops and Albertaceratops. Considered together, both phylogenetic methods unequivocally place Machairoceratops as an early-branching centrosaurine, and given the biostratigraphic position of Machairoceratops, these details increase the known ceratopsid diversity from both the Wahweap Formation and the southern portion of Laramidia. Finally, the unique morphology of the parietal ornamentation highlights the evolutionary disparity of frill ornamentation near the base of Centrosaurinae.

Vertebrate microfossil assemblages contain abundant fossil material of small and large bodied animals recruited from the local paleocommunity that can provide important information for reconstructing regional paleoecology. The Foremost Formation is the oldest unit of the Belly River Group, and records the transition from the fully marine shales of the Pakowki Formation to the non-marine strata of the relatively well-sampled Oldman and Dinosaur Park formations. Although the Foremost Formation has relatively limited exposure and vertebrate fossil material is not abundant, it does contain some important early records of major vertebrate clades from Laramidia (e.g. ceratopsids, pachycephalosaurids). Here we document a new microfossil locality from the upper part of the formation that shows a transitional assemblage containing an abundance of terrestrial forms such as dinosaurs and other sauropsids, while still showing considerable marine influence. The proportion of marine taxa at this site is reduced relative to most sites known from the Foremost Formation, though much higher than more terrestrial sites of the overlying Oldman Formation. In addition to filling a gap in our understanding of this paleoenvironmental transition, this new site preserves two particularly significant specimens: a large, complete, cephalic spine of the hybodont shark Hybodus , and jaw fragments from the ratfish Elasmodus . This represents the first known complete cephalic spine of a hybodont shark from the Cretaceous of Alberta. The ratfish jaw fragments represent the first published record of this group from the Foremost Formation, further increasing our knowledge of chondrichthyan diversity in the Western Interior Seaway. Comparisons of this site to other microsites from the Campanian of Alberta demonstrate the utility of certain key groups, such as lissamphibians and chondrichthyans, in determining paleoenvironments from Mesozoic and Cenozoic vertebrate microsite assemblage data.

Two partial “macrobaenid” shells are described from a single Late Paleocene (Clarkforkian 1) quarry at Burns Mine near Washoe, Carbon County, Montana, USA, and are referred to “Clemmys” backmani, a taxon typified in the Paleocene Ravenscrag Formation of Saskatchewan, Canada. Though tentative, morphological, temporal and spatial arguments highlight similarities between “Clemmys” backmani and the Campanian taxon Judithemys sukhanovi, and we therefore suggest the new combination Judithemys backmani. Judithemys sukhanovi and Judithemys backmani both originate from the eastern margins of the western landmass Laramidia and exhibit a pronounced ridge along the visceral side of the first costal and C-shaped bridge peripherals into which the flat thoracic ribs insert superficially, characters that must be interpreted as symplesiomorphies. By contrast, the coeval taxon Osteopygis emarginatus originates from the eastern shores of the eastern landmass Appalachia, lacks the visceral ridge of the first costal, and possesses massive, triangular peripherals into which the peglike thoracic ribs insert deeply.

Previous biogeographic studies of late Cretaceous (late Campanian) vertebrate faunas in the Western Interior Basin (WIB) of North America have suggested the presence of faunal and floral provincialism, characterized by distinct northern and southern ‘biomes.’ However, the “provincialism hypothesis” has been questioned based largely on the contention that the investigated faunas were recovered from a series of diachronous, time-transgressive deposits, and are therefore non-correlative. Extensive work in several fossiliferous units of late Campanian age, including the Dinosaur Park, Judith River, Two Medicine, Kaiparowits, Fruitland/Kirtland, and Aguja formations, has greatly increased understanding of WIB vertebrate faunas and their chronostratigraphic relationships. Here updated and greatly expanded faunal and chronostratigraphic datasets are utilized to undertake an extensive biogeographic analysis of these six terrestrial fossiliferous formations within the WIB of North America. Quantitative biogeographic comparisons of the formations and their constituent faunas are conducted using four statistical methods: Analysis of Similarity, Q-mode cluster analysis, Parsimony Analysis of Endemicity, and Correspondence Analysis. The results of this study provide strong support for highly divergent faunas in northern and southern regions of the WIB, with a latitudinal faunal gradient as an interface. Yet the nature of the interface between these faunas remains unclear, with possibilities including: 1) two or more discrete provinces separated by a zone (or zones) of faunal mixing; and 2) a continuous latitudinal gradient or cline, with no discrete zones of endemism. Lacking evidence of any physiographic barrier to north–south dispersal, climatic variation within the WIB is regarded as the most likely explanation for the overarching biogeographic patterns observed for late Campanian vertebrate taxa.

Skeletal remains of Late Cretaceous (Campanian and Maastrichtian) tyrannosauroids are rare in southwestern North America (Carr and Williamson, 2000). Historically, the identity and diversity of sou...

Most dromaeosaurids were small- to medium-sized cursorial, scansorial, and arboreal, sometimes volant predators, but a comparatively small percentage grew to gigantic proportions. Only two such giant “raptors” have been described from North America. Here, we describe a new giant dromaeosaurid, Dakotaraptor steini gen. et sp. nov., from the Hell Creek Formation of South Dakota. The discovery represents the first giant dromaeosaur from the Hell Creek Formation, and the most recent in the fossil record worldwide. A row of prominent ulnar papilli or “quill knobs” on the ulna is our first clear evidence for feather quills on a large dromaeosaurid forearm and impacts evolutionary reconstructions and functional morphology of such derived, typically flight-related features. The presence of this new predator expands our record of theropod diversity in latest Cretaceous Laramidia, and radically changes paleoecological reconstructions of the Hell Creek Formation.

Laser-fusion 40Ar/39Ar analysis of four bentonite horizons produces the first absolute ages for the 860-m-thick Kaiparowits Formation and resolves previous age uncertainty caused by ambiguous biostratigraphy. A late Campanian (Judithian) age of ca. 76.1–74.0 Ma is determined, resulting in a high-resolution temporal framework for the richly fossiliferous formation. Detailed stratigraphic correlation reveals that the Kaiparowits Formation is contemporaneous with many of the most important vertebrate fossil-bearing formations in the Western Interior Basin, and with other well-studied strata across Utah and southeastern Wyoming, including portions of the Book Cliffs sequence. The Judithian age determination and correlations for the Kaiparowits Formation presented here provide a new chronological basis for addressing questions relating to mammal biostratigraphy, vertebrate evolution, biodiversity and paleobiogeography (e.g., dinosaur provincialism) in the Cretaceous Western Interior Basin.

A fragmentary skeleton from the Kaiparowits Formation (Upper Campanian) of southern Utah represents a new taxon of chelydroid turtle herein named Lutemys warreni. Lutemys warreni differs from other chelydroids in the presence of a smooth shell, lack of plastral or carapacial fontanelles, and development of a thin, gracile plastron. A maximum parsimony analysis of all Late Cretaceous and early Paleogene chelydroids from Laramidia suggests that L. warreni is the most basal known stem kinosternoid. Lutemys warreni therefore represents the fourth named pan-kinosternoid from the Late Cretaceous western island landmass of Laramidia and the first named pan-kinosternoid from the Kaiparowits Formation. The description of L. warreni increases the taxonomic diversity of the Kaiparowits Formation to 16 turtle taxa, making it one of the most diverse fossil turtle assemblages.http://zoobank.org/urn:lsid:zoobank.org:pub:C199E9AE-6F3C-442A-AA12-3960B28F4066SUPPLEMENTAL DATA—Supplemental materials are available fo...

Megaherbivorous dinosaurs were exceptionally diverse on the Late Cretaceous island continent of Laramidia, and a growing body of evidence suggests that this diversity was facilitated by dietary niche partitioning. We test this hypothesis using the fossil megaherbivore assemblage from the Dinosaur Park Formation (upper Campanian) of Alberta as a model. Comparative tooth morphology and wear, including the first use of quantitative dental microwear analysis in the context of Cretaceous palaeosynecology, are used to infer the mechanical properties of the foods these dinosaurs consumed. The phylliform teeth of ankylosaurs were poorly adapted for habitually processing high-fibre plant matter. Nevertheless, ankylosaur diets were likely more varied than traditionally assumed: the relatively large, bladed teeth of nodosaurids would have been better adapted to processing a tougher, more fibrous diet than the smaller, cusp-like teeth of ankylosaurids. Ankylosaur microwear is characterized by a preponderance of pits and scratches, akin to modern mixed feeders, but offers no support for interspecific dietary differences. The shearing tooth batteries of ceratopsids are much better adapted to high-fibre herbivory, attested by their scratch-dominated microwear signature. There is tentative microwear evidence to suggest differences in the feeding habits of centrosaurines and chasmosaurines, but statistical support is not significant. The tooth batteries of hadrosaurids were capable of both shearing and crushing functions, suggestive of a broad dietary range. Their microwear signal overlaps broadly with that of ankylosaurs, and suggests possible dietary differences between hadrosaurines and lambeosaurines. Tooth wear evidence further indicates that all forms considered here exhibited some degree of masticatory propaliny. Our findings reveal that tooth morphology and wear exhibit different, but complimentary, dietary signals that combine to support the hypothesis of dietary niche partitioning. The inferred mechanical and dietary patterns appear constant over the 1.5 Myr timespan of the Dinosaur Park Formation megaherbivore chronofauna, despite continual species turnover.

The Late Cretaceous (∼95-66 million years ago) western North American landmass of Laramidia displayed heightened non-marine vertebrate diversity and intracontinental regionalism relative to other latest Cretaceous Laurasian ecosystems. Processes generating these patterns during this interval remain poorly understood despite their presumed role in the diversification of many clades. Tyrannosauridae, a clade of large-bodied theropod dinosaurs restricted to the Late Cretaceous of Laramidia and Asia, represents an ideal group for investigating Laramidian patterns of evolution. We use new tyrannosaurid discoveries from Utah--including a new taxon which represents the geologically oldest member of the clade--to investigate the evolution and biogeography of Tyrannosauridae. These data suggest a Laramidian origin for Tyrannosauridae, and implicate sea-level related controls in the isolation, diversification, and dispersal of this and many other Late Cretaceous vertebrate clades.

While centrosaurines and ceratopsids in general are abundant in the Late Campanian of northern Laramidia, they are much less commonly found in southern Laramidia. This has supported hypotheses of dinosaur provinciality and endemism in the Late Cretaceous with the delineation of at least two separate faunal zones, north and south Laramidia. There have been 12 genera of centrosaurines recognized from northern Laramidia while two genera, Diabloceratops and Nasutoceratops, have been named from southern Laramidia. We present an osteological description and taphonomic outline for a new centrosaurine ceratopsid from the Aguja Formation of northern Coahuila, Mexico that is not currently diagnosable to the generic level, but likely represents a new taxon. Further, we have included three-dimensional surface scans of all material attributed to this animal. Considering the large number of centrosaurines from northern Laramidia, it is likely that cladistic analyses are biased towards this faunal zone. New findings of southern centrosaurines are needed to correct this bias. This discovery expands the range of centrosaurines south to Coahuila, Mexico and adds new information to better characterize the morphology and taxonomy of centrosaurines from southern Laramidia and their evolution in comparison to their northern counterparts.

Eotrachodon orientalis gen. et sp. nov. (latest Santonian of Alabama, southeastern U.S.A.) is one of the oldest and most basal hadrosaurid dinosaurs and the only hadrosaurid from Appalachia (present day eastern North America) with a preserved skull. This taxon possesses a relatively derived narial structure that was until now regarded as synapomorphic for saurolophine (solid-crested or crestless) hadrosaurids. Maximum parsimony analysis places E. orientalis as the sister taxon to Saurolophidae (Saurolophinae + Lambeosaurinae). Character optimization on the phylogeny indicates that the saurolophine-like circumnarial structure evolved by the Santonian following the split between saurolophines and lambeosaurines but prior to the major hadrosaurid radiation. Statistical dispersal-vicariance analysis posits an Appalachian ancestral area for Hadrosauridae and subsequent dispersal of their ancestors into Laramidia (present-day western North America) during the Cenomanian.http://zoobank.org/urn:lsid:zooba...

BackgroundDuring much of the Late Cretaceous, a shallow, epeiric sea divided North America into eastern and western landmasses. The western landmass, known as Laramidia, although diminutive in size, witnessed a major evolutionary radiation of dinosaurs. Other than hadrosaurs (duck-billed dinosaurs), the most common dinosaurs were ceratopsids (large-bodied horned dinosaurs), currently known only from Laramidia and Asia. Remarkably, previous studies have postulated the occurrence of latitudinally arrayed dinosaur "provinces," or "biomes," on Laramidia. Yet this hypothesis has been challenged on multiple fronts and has remained poorly tested.Methodology/principal findingsHere we describe two new, co-occurring ceratopsids from the Upper Cretaceous Kaiparowits Formation of Utah that provide the strongest support to date for the dinosaur provincialism hypothesis. Both pertain to the clade of ceratopsids known as Chasmosaurinae, dramatically increasing representation of this group from the southern portion of the Western Interior Basin of North America. Utahceratops gettyi gen. et sp. nov.-characterized by short, rounded, laterally projecting supraorbital horncores and an elongate frill with a deep median embayment-is recovered as the sister taxon to Pentaceratops sternbergii from the late Campanian of New Mexico. Kosmoceratops richardsoni gen. et sp. nov.-characterized by elongate, laterally projecting supraorbital horncores and a short, broad frill adorned with ten well developed hooks-has the most ornate skull of any known dinosaur and is closely allied to Chasmosaurus irvinensis from the late Campanian of Alberta.Conclusions/significanceConsidered in unison, the phylogenetic, stratigraphic, and biogeographic evidence documents distinct, co-occurring chasmosaurine taxa north and south on the diminutive landmass of Laramidia. The famous Triceratops and all other, more nested chasmosaurines are postulated as descendants of forms previously restricted to the southern portion of Laramidia. Results further suggest the presence of latitudinally arrayed evolutionary centers of endemism within chasmosaurine ceratopsids during the late Campanian, the first documented occurrence of intracontinental endemism within dinosaurs.

We describe the first diagnostic dinosaur fossil from Washington State. The specimen, which consists of a proximal left femur, was recovered from the shallow marine rocks of the Upper Cretaceous (Campanian) Cedar District Formation (Nanaimo Group) and is interpreted as pertaining to a large theropod on the basis of its hollow medullary cavity and proximally placed fourth trochanter. The Washington theropod represents one of the northernmost occurrences of a Mesozoic dinosaur on the west coast of the United States and one of only a handful from the Pacific coast of Laramidia during the Cretaceous. Its isolated nature and preservation in marine rocks suggest that the element was washed in from a nearby fluvial system. If the femur pertains to a tyrannosauroid, which seems likely given its size and the widespread occurrence of the group across Laramidia during Late Cretaceous times, then it would represent an earlier occurrence of large body size than previously recognized (complete femur length estimated at 1.2 meters). Uncertainty surrounding the latitude of deposition of the Nanaimo Group (i.e., the Baja-British Columbia hypothesis) precludes assigning the Washington theropod to either of the putative northern or southern biogeographic provinces of Laramidia.

The question of what role differential jaw mechanics may have played in facilitating dietary niche partitioning among Late Cretaceous megaherbivorous dinosaurs from Laramidia is examined, using the fossil assemblage of the Dinosaur Park Formation as a test case. We use phylogenetic inference to reconstruct the mandibular adductor musculature of these animals, which we then apply to the construction of biomechanical lever models of the mandible to estimate relative bite forces. Our findings reveal predictably weak bite forces in ankylosaurs, and comparatively high bite forces in ceratopsids and hadrosaurids, both of which possessed a mechanical advantage that produced bite forces 2–3 times higher than those forces exerted by the adductor musculature. The impressive jaw mechanism shared by the last two taxa evolved in a stepwise fashion, independently in each lineage. There is tentative evidence to suggest that nodosaurids had more powerful bites than ankylosaurids, but the overall mechanical divers...

During Late Maastrichtian time, three major sedimentary depositional provinces existed in continental environments of the western interior region of North America. The sediments accumulated within these provinces are herein termed the piedmont, alluvial plain, and coastal lowland lithosomes. These sedimentary lithosomes correspond to broad paleoenvironmental and paleophysiographic provinces that resulted from the westward shift of the Pacific coast, the bisection and retreat of the interior epeiric sea, and the development of an intermontane basin system during Maastrichtian time. These dramatic physiographic changes created environments markedly different from those that had prevailed during most of the Late Cretaceous, when western North America consisted of a narrow peninsula flanked on the east by a remarkably stable and monotonous coastal plain. In conjunction with these physiographic and environmental changes, three diverse dinosaur-dominated continental vertebrate faunas arose, herein termed the Leptoceratops, Triceratops, and Alamosaurus faunas. Each was peculiar to a sedimentary/environmental province and among them there was little interchange. The separation of these faunas indicates that the dinosaur-dominated communities had adapted to changing or “deteriorating” environmental conditions at the close of Cretaceous time. The Alamosaurus fauna characterized markedly seasonal, semi-arid, environments of the intermontane basins south of about 35°N latitude. The Triceratops fauna inhabited humid coastal floodplains and swamps bordering the retreating northern embayment of the epeiric sea, north of latitude 35°N. The Leptoceratops fauna inhabited cool piedmont environments flanking the mountainous Cordilleran Overthrust Belt north of 35°N latitude. Recognition of this biogeographic zonation indicates that the Triceratops biozone is only of local utility, and that the biostratigraphy of Upper Cretaceous continental deposits in North America must reflect the provincialism now recognized. Moreover, the evident adaptability of dinosaur faunas to varied and changing environmental conditions suggests that climatic change alone may not have been responsible for their demise.

The osteology of the hadrosaurid dinosaur Kritosaurus navajovius (late Campanian of southern North America) is documented in detail, and the taxonomy and phylogenetic relationships of the genus are revised. Kritosaurus is rediagnosed based on the extensive length of the dorsolateral margin of the maxilla and a unique combination of characters that includes a jugal with orbital constriction deeper than infratemporal one, infratemporal fenestra greater than orbit and with dorsal margin greatly elevated above dorsal orbital margin in adults, frontal participating in orbital margin, and paired caudal parasagittal processes of nasals resting over frontals. The taxonomy of numerous hadrosaurid specimens previously referred to Kritosaurus is reassessed; the vast majority of these cannot be positively referred to Kritosaurus. One exception is a specimen collected from the Cerro del Pueblo Formation that extends the geographical range of K. navajovius further south in Laramidia, to present-day northern Mexico. Ana...

Herbivore coexistence on the Late Cretaceous island continent of Laramidia has been a topic of great interest, stemming from the paradoxically high diversity and biomass of these animals in relation to the relatively small landmass available to them. Various hypotheses have been advanced to account for these facts, of which niche partitioning is among the most frequently invoked. However, despite its wide acceptance, this hypothesis has not been rigorously tested. This study uses the fossil assemblage from the Dinosaur Park Formation of Alberta as a model to investigate whether niche partitioning facilitated herbivorous dinosaur coexistence on Laramidia. Specifically, the question of feeding height stratification is examined in light of the role it plays in facilitating modern ungulate coexistence. Most herbivorous dinosaur species from the Dinosaur Park Formation were restricted to feeding no higher than approximately 1 m above the ground. There is minimal evidence for feeding height partitioning at this level, with ceratopsids capable of feeding slightly higher than ankylosaurs, but the ecological significance of this is ambiguous. Hadrosaurids were uniquely capable of feeding up to 2 m quadrupedally, or up to 5 m bipedally. There is no evidence for either feeding height stratification within any of these clades, or for change in these ecological relationships through the approximately 1.5 Ma record of the Dinosaur Park Formation. Although we cannot reject the possibility, we find no good evidence that feeding height stratification, as revealed by reconstructed maximum feeding heights, played an important role in facilitating niche partitioning among the herbivorous dinosaurs of Laramidia. Most browsing pressure was concentrated in the herb layer, although hadrosaurids were capable of reaching shrubs and low-growing trees that were out of reach from ceratopsids, ankylosaurs, and other small herbivores, effectively dividing the herbivores in terms of relative abundance. Sympatric hadrosaurids may have avoided competing with one another by feeding differentially using bipedal and quadrupedal postures. These ecological relationships evidently proved to be evolutionarily stable because they characterize the herbivore assemblage of the Dinosaur Park Formation through time. If niche partitioning served to facilitate the rich diversity of these animals, it may have been achieved by other means in addition to feeding height stratification. Consideration of other feeding height proxies, including dental microwear and skull morphology, may help to alleviate problems of underdetermination identified here.